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Re: CALCIUM CARBONATE VIS CALCIUM GLYCINATE » freedom2001

Posted by Larry Hoover on August 29, 2003, at 7:42:12

In reply to CALCIUM CARBONATE VIS CALCIUM GLYCINATE, posted by freedom2001 on August 29, 2003, at 0:23:30

> The calcium in Coral Calcium is mostly calcium carbonate, which provides the highest amount of calcium absorbed per unit volume.

That's incorrect. It has one of the highest elemental mass percentages of calcium. It is relatively poorly absorbed, however, and directly impacts stomach acid levels. Eat some powdered chalk (calcium carbonate) and see if your stool turns white. Guess what's happening?

> CaCO3 is 40 w/o

(is that meant to be weight percent?)

> calcium and is quite dense. Many manufacturers claim higher calcium absorption on a percent basis for low density products like calcium glycinate.

Quite correct, because the calcium is completely soluble, a prerequisite for absorption.


Am J Ther. 1999 Nov;6(6):313-21.

Comment in:
Am J Ther. 2001 Jan-Feb;8(1):73-4.
Am J Ther. 2001 Jan-Feb;8(1):74-7.

Meta-analysis of calcium bioavailability: a comparison of calcium citrate with calcium carbonate.

Sakhaee K, Bhuket T, Adams-Huet B, Rao DS.

University of Texas Southwestern Medical School, Center for Mineral Metabolism and Clinical Research, Dallas, TX 75235-8891, USA.

OBJECTIVE: To perform a meta-analysis of data from available published trials comparing the bioavailability of calcium carbonate with that of calcium citrate. DATA SOURCES: The whole set was comprised of 15 studies involving 184 subjects who underwent measurement of calcium absorption from calcium carbonate and calcium citrate. Category A excluded four studies for lack of physiological relevance, use of a mixed preparation with low content of calcium carbonate, or wide variability in results. Category B was comprised of five studies (from Category A) involving 71 subjects who took calcium supplements on an empty stomach. Category C was comprised of six studies (from Category A) involving 65 subjects who took calcium preparations with meals. METHOD: The meta-analysis of calcium absorption data from calcium carbonate and calcium citrate, with calculation of effect size and 95% confidence intervals. RESULTS: Calcium absorption from calcium citrate was consistently significantly higher than that from calcium carbonate by 20.0% in the whole set, by 24.0% in Category A, by 27.2% on an empty stomach, and by 21.6% with meals. CONCLUSION: Calcium citrate is better absorbed than calcium carbonate by approximately 22% to 27%, either on an empty stomach or co-administered with meals.


However, if stomach acid secretion is impaired (due to aging, vitamin deficiency, or acid-reducing drugs (Zantac, Pepcid, Nexxium, etc.)), things get even worse. Note that in achlorhydric subjects, fractional absorption of calcium from the citrate is about 45%, whereas that from the carbonate is about 5%.


N Engl J Med. 1985 Jul 11;313(2):70-3.

Calcium absorption and achlorhydria.

Recker RR.

Defective absorption of calcium has been thought to exist in patients with achlorhydria. I compared absorption of calcium in its carbonate form with that in a pH-adjusted citrate form in a group of 11 fasting patients with achlorhydria and in 9 fasting normal subjects. Fractional calcium absorption was measured by a modified double-isotope procedure with 0.25 g of calcium used as the carrier. Mean calcium absorption (+/- S.D.) in the patients with achlorhydria was 0.452 +/- 0.125 for citrate and 0.042 +/- 0.021 for carbonate (P less than 0.0001). Fractional calcium absorption in the normal subjects was 0.243 +/- 0.049 for citrate and 0.225 +/- 0.108 for carbonate (not significant). Absorption of calcium from carbonate in patients with achlorhydria was significantly lower than in the normal subjects and was lower than absorption from citrate in either group; absorption from citrate in those with achlorhydria was significantly higher than in the normal subjects, as well as higher than absorption from carbonate in either group. Administration of calcium carbonate as part of a normal breakfast resulted in completely normal absorption in the achlorhydric subjects. These results indicate that calcium absorption from carbonate is impaired in achlorhydria under fasting conditions. Since achlorhydria is common in older persons, calcium carbonate may not be the ideal dietary supplement.


> A lot of this is deceptive marketing.

No, it's backed by science.

> A capsule of calcium carbonate will result in more calcium in your bloodstream than a same-size capsule of any other form of
calcium.

That is false, on its face. Moreover, the binders in the calcium carbonate may present yet another problem with absorption.


Calcif Tissue Int. 1991 Nov;49(5):308-12.

Comment in:
Calcif Tissue Int. 1992 Feb;50(2):197.

In vitro dissolution of calcium carbonate preparations.

Brennan MJ, Duncan WE, Wartofsky L, Butler VM, Wray HL.

Department of Medicine, Walter Reed Army Medical Center, Washington, DC 20307-5001.

Calcium supplements are widely used for the treatment of osteoporosis. The bioavailability of these preparations is unknown. Because poor tablet dissolution accounts for a majority of drug bioavailability problems, we determined the in vitro dissolution at 30, 60, and 90 minutes of 27 commercially available calcium carbonate supplements using the method of the U.S. Pharmacopoiea. At 30 minutes, five preparations (18%) were more than 75% dissolved, four (15%) between 33 and 74%, and the remaining 18 (67%) were less than 33% dissolved. After 90 minutes, 17 (63%) of the preparations were less than 50% dissolved. Dissolution correlated negatively with the weight of filler (noncalcium carbonate material in the tablet) (rs = -0.51, P less than 0.01) but not with tablet hardness or cost. Similar to previous studies, we also found no correlation of dissolution with the stated calcium content, chemical source of calcium carbonate (oyster shell or chemical precipitate), or retail source. We conclude that there is a wide range of in vitro dissolution among the calcium carbonate preparations tested, and that the filler is an important determinant of the dissolution of these tablets. These results raise concern about the bioavailability of the calcium in these preparations and may have important implications for the therapeutic use of the various calcium carbonate supplements.


For those on thyroid replacement, be wary of the following:

Thyroid. 2001 Oct;11(10):967-71.

The acute effect of calcium carbonate on the intestinal absorption of levothyroxine.

Singh N, Weisler SL, Hershman JM.

Department of Endocrinology and Metabolism, Veterans Affairs Greater Los Angeles Healthcare System, California 90073, USA. Nalini.Singh@med.va.gov

To determine the acute effect of calcium, we measured levothyroxine absorption after ingestion of thyroxine (T4) with and without simultaneous ingestion of calcium (as calcium carbonate) in seven volunteers without thyroid disease. Serum total T4, total triiodothyronine (T3), free T4, and thyrotropin (TSH) levels were measured after ingestion of 1,000 microg of levothyroxine on two separate visits at 4-week intervals: (1) levothyroxine alone and (2) levothyroxine together with 2.0 g of calcium as calcium carbonate. The amount of absorbed levothyroxine was calculated as the incremental rise in serum T4 level during the first 6 hours multiplied by the volume of distribution for the hormone. When 1,000 microg of levothyroxine alone was given to subjects, the maximum average total T4 absorption was 837 microg (83.7% of the dose ingested) at 120 minutes. When levothyroxine was coadministered with 2.0 g of calcium (as calcium carbonate), the maximum average T4 absorption decreased to 579 microg (57.9% of the dose ingested) at 240 minutes. The total levothyroxine absorption over 6 hours was significantly greater with thyroxine than that with thyroxine and calcium (p = 0.02). The administration of calcium and levothyroxine in these subjects was associated with a significant reduction in the peak increment in serum total T4 (p = 0.02) and free T4 levels (p = 0.03), as well as a significant reduction in the overall increment in serum total T4 (p = 0.003), free T4 (p = 0.002), and total T3 levels (p = 0.01) over four time points (120 minutes, 240 minutes, 360 minutes, 1,440 minutes). In summary, this pharmacokinetic study in seven volunteers indicates that calcium carbonate acutely reduces T4 absorption.

Lar

 

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